President Donald Trump yesterday turned up the heat on North Korea, warning Pyongyang that the US military is "locked and loaded" in the event of a misstep by the totalitarian state, despite mounting international calls for restraint.

Trump launched another salvo at the regime of Kim Jong-Un to keep its nuclear weapons and ballistic missile programs in check, as the North's official news agency accused the US of driving the situation "to the brink" of war.

The latest Twitter threat from the Republican billionaire leader came as concerns swelled worldwide that a miscalculation by either side could trigger a catastrophic conflict on the Korean peninsula.

"Military solutions are now fully in place, locked and loaded, should North Korea act unwisely. Hopefully Kim Jong Un will find another path!" Trump wrote from his golf club retreat in New Jersey, where he is spending two weeks.

The official KCNA news service countered in an editorial that "Trump is driving the situation on the Korean peninsula to the brink of a nuclear war," calling the US "the mastermind of nuclear threat, the heinous nuclear war fanatic."

Earlier yesterday, China -- Pyongyang's main diplomatic ally -- had urged Trump and Kim to tone down the sabre-rattling.

Chinese foreign ministry spokesman Geng Shuang called on both sides to avoid "going down the old path of alternately showing strength and continuously escalating the situation."

"We call on the relevant parties to be cautious with their words and actions, and contribute more toward easing tensions and enhancing mutual trust," Geng said in a statement.

Russia's Foreign Minister Sergei Lavrov said Moscow was "very alarmed" at Trump's tough talk, saying Washington should take the first step toward cooling tensions.

"When a fight has nearly broken out, the first step away from the dangerous threshold should be taken by the side that is stronger and smarter," Lavrov said.

Beijing has repeatedly pushed resuming long-dormant six-party talks to peacefully resolve the mounting tensions, but its position has been overshadowed by Trump and Kim's emerging game of brinkmanship.

China's proposal for North Korea to halt its weapons programs in exchange for a suspension of military drills by the United States and South Korea -- seen by Pyongyang as provocative -- has essentially been ignored.

Trump has progressively ramped up the tone throughout the week -- after brandishing a threat of unleashing "fire and fury" on North Korea, he said Thursday maybe that statement "wasn't tough enough."

He warned Pyongyang it should be "very, very nervous" of the consequences if it even thinks of attacking US soil, after Kim's regime said it was readying plans to launch missiles towards the US Pacific territory of Guam.

Trump also called on China to "do a lot more" to heap pressure on Kim.

German Chancellor Angela Merkel joined the intensifying chorus of calls for restraint, saying diplomacy was the answer.

"Germany will very intensively take part in the options for resolution that are not military but I consider a verbal escalation to be the wrong response," she said.

Nearly a week ago, the UN Security Council unanimously passed fresh sanctions against Pyongyang over its weapons program, including export bans, a new punishment that could cost North Korea $1 billion a year.

US Defense Secretary Jim Mattis appeared intent Thursday on easing the tension, describing the prospect of war as "catastrophic" and saying diplomacy remained the priority.

Asked yesterday if Mattis was aware of Trump's latest tweet, spokesman Colonel Rob Manning simply said the Pentagon chief was "in close and constant contact with the president."

Concerning the prospect of forthcoming military action, Manning told AFP: "We maintain a high state of readiness to deal with the North Korean threat in conjunction with our allies and partners in the region."

A White House official noted: "There are military plans for just about any crisis we may face in the world. (...) This isn't anything new."

In China, the state-run Global Times yesterday said that Beijing should not intervene on Pyongyang's side if it triggered a conflict.

Beijing should "make clear that if North Korea launches missiles that threaten US soil first and the US retaliates, China will stay neutral," it said in an editorial.

Meanwhile in South Korea, calls mounted for Seoul to develop atomic weapons of its own, with the Korea Herald saying in an editorial: "Now is time to start reviewing nuclear armament."

Relations between Washington and Pyongyang have been tense for months, in the wake of the North's repeated missile tests, including two successful intercontinental ballistic missile (ICBM) test launches in July that brought much of the US mainland within range.

North Korea raised hackles in the United States when it announced a detailed plan to send four missiles over Japan and towards Guam, an island territory of some 165,000 people, where some 6,000 US soldiers are based.

Pyongyang said the scheme to target the island, a key US military outpost in the western Pacific, was intended to "signal a crucial warning" as "only absolute force" would have an effect on a US leader "bereft of reason."

The tough talk has caused global markets to plunge this week, with stocks in the red again yesterday.

Tensions on the Korean peninsula tend to increase when Seoul and Washington launch major military joint exercises, and the next, Ulchi Freedom Guardian, is set to kick off around August 21.